The present invention relates generally to a dimming circuit for use with electronic ballasts driving fluorescent lamps.
In the past, fluorescent lamp ballasts have not readily been able to accommodate dimming. Prior art dimming approaches have often utilized continuously adjustable dimming, with the consequent increase in cost and complexity. More recently, it has been found desirable to provide for a single dimming level such that fluorescent lamps may be operated either at full brightness or at a reduced brightness, for example 50% illumination. At least one state has a requirement for such reduced level illumination availability; it has also been found desirable in applications where full brightness may be utilized under some circumstances such as during normal working hours, and where a reduced brightness may be suitable at other times, for example during after hours cleaning, or while using cathode ray terminals.
Prior art systems have not been able to provide such dimming from a single control voltage, nor have such prior art systems taken into account the varying needs in the fluorescent lamp filament circuit during dimming conditions.